The present invention relates to photosensitive material for electrophotography having a surface protection layer on a photosensitive layer for use in electrophotographic devices such as digital copiers and printers.
Since the light source used for these devices is normally a semiconductor layer (LD), a light emitting element (LED) or a combination of an ordinary light source such as a halogen lamp and a liquid crystal shutter (LCS), and the wave length is long, e.g., from 660 to 800 nm, photosensitive material of this kind has generally consisted of a carrier generation layer having sensitivity to such a light source, a carrier transport layer for transporting generated carriers and a surface protection layer for protecting against external objects such as paper or toner. Furthermore, the printing resistance of the photosensitive material is determined by the quality of the surface protection layer.
However, in conventional photosensitive materials, the surface protection layer as well as the carrier generation layer deteriorate after printing about 80,000 to 100,000 sheets and the photosensitive material becomes unusable. Accordingly, surface protection layers made of selenium have been modified by increasing their thickness or changing their composition from pure selenium to a selenium alloy containing 5 to 8 wt % tellurium or selenium alloy containing less than 5 wt % arsenic. The working life of such a surface protection layer is still only about 100,000 to 200,000 sheets. Accordingly, although such modified materials can be used in medium to low speed printers or digital copiers, they are not suitable for high speed digital copiers or printers. Therefore, photosensitive material which increases the printing resistance by using amorphous silicon instead of selenium-type material for the photosensitive layer has been used in the high speed type printers. However, since the amorphous silicon photosensitive material cannot be used without a heater inside the printer, this material is extremely difficult and expensive to use.
Accordingly, the object of the present invention is to overcome the foregoing problems and provide photosensitive material for use in electrophotography that can be used for high speed printers or digital copiers, by increasing the printing resistance as a result of improvement in a selenium-based surface protection layer.